With a gas supply system with which liquefied gas is vaporized, it has been conventionally practiced to heat the pipe passage to more than a specified temperature to prevent the supply gas from re-condensing in the pipe passage. Similarly, with a gas exhaust system in semiconductor manufacturing facilities, plasma generating apparatuses and the like, the pipe passages, valve devices mounted thereon, and the like, have been heated to prevent exhaust gas from forming gas condensation in the pipe passage.
For example, the internal pressure of a process chamber for semiconductor manufacturing facilities can be kept evacuated to approximately 10−4 to 102 torr, depending on the type of the process, by making the exhaust side of the chamber continuously exhausted by a vacuum pump. On the other hand, because necessary treatments are performed by using various kinds of corrosive gases or toxic gases, a large amount of corrosive gases, and the like, are found in the exhaust gases passing through the exhaust system. Accordingly, for an exhaust system for the process chamber, condensation of the corrosive gas is prevented by heating pipe passages or valve units; thus, the devices constituting the exhaust system are prevented from corrosion because corrosive effects are substantially increased when corrosive gases liquefy due to condensation.
Also, with semiconductor manufacturing facilities, it is strongly desired that the entire unit, including the exhaust system of the process chamber, be further downsized. Therefore, for the vacuum exhaust system of the process chamber, it is also strongly desired to make small the diameter of the exhaust pipe passage, downsize the vacuum exhaust pumps, downsize valves to be employed, and the like are, and ideas to realize these desires have been studied. Particularly, for the vacuum exhaust system, more effort has been made to further downsize the pipe passages and valves by enhancing their thermal insulating performance.
With regard to the pipe passages of the vacuum exhaust system in semiconductor manufacturing facilities and the like, the initial objective has been nearly achieved by employing a vacuum thermal insulating pipe passage. However, with regard to a valve unit that constitutes a vacuum exhaust system, there remain many unsolved problems, such as thermal insulating capabilities, downsizing, energy-saving and the like.
Though the explanation given here is with regard to problems related to the vacuum exhaust system for semiconductor manufacturing facilities, it goes without saying, however, that such problems have some similarities with the problems of the gas supply system on the upstream side, and the gas supply system or gas exhaust system in other chemical apparatuses, and the like. Accordingly, the gas supply system, exhaust system for semiconductor manufacturing facilities, and the like, are used as examples to explain these problems as follows.
A so-called “unit-type valve” V, constituted as shown in FIG. 17 to FIG. 20, has been widely used for semiconductor manufacturing facilities and the like to make a valve that is small and compact. For example, the unit-type valve V shown in FIG. 17 and FIG. 18 has outer dimensions of 150˜500 mm in breadth, 130˜150 mm in height, and 80˜100 in depth. In particular, the valve V is made of a valve unit body V1 formed by combining a plural number of valve bodies V10, V20 . . . , and actuators D mounted on the valve bodies V10, V20 . . . , respectively. The valve itself, as a unit, is a metal diaphragm type valve comprising the valve body V10 and the actuator D. The afore-mentioned valve V is heated to normally approximately 150° C. by a heater (not illustrated) to prevent corrosive gases passing through the inside from condensing.
The heated valve V is of a very compact structure, and its temperature is held at less than a temperature (approximately 40° C.) that allows it to be touched by hands from the outside. And, heated valve V needs thermal insulation so that leakage of heat directly to the outside is prevented. In the case where rock wool is used as a thermal insulating material, the thickness of the wool needed for one side will be 30 to 50 mm, thus making it difficult to compact-size the valve V.
Similarly, in the case where the valve V is made to be enclosed by a pneumatic thermal insulation type box body (equipped with a silver-plated layer to suppress heat transfer by radiation on the inner wall surface and made with an air layer of 10 mm) of a double wall structure, it was difficult to reduce the temperature of the outer surface of the thermal insulating box to less than approximately 40° C. because of heat transfer by convection of the air layer.
Therefore, first, the inventors of the present invention developed a vacuum thermal insulating valve, which was made to house a valve unit body V1 of the valve inside a vacuum thermal insulating box S, by making use of vacuum thermal insulation as shown in FIG. 21. It was learned, however, that the vacuum thermal insulating valve in FIG. 21 was not commercially practical because the temperature of the outer surface (i.e., the surface temperature of the actuator in the center part) became higher than the specified temperature (40° C.).
Therefore, inventors of the present invention formed a vacuum thermal insulating box S made by combining 3 vacuum jackets S1, S2, S3 as shown in FIG. 22 to FIG. 25, and conducted various kinds of tests using this box. In FIG. 22 to FIG. 25, the main reasons why the vacuum thermal insulating box S is divided into 3 vacuum jackets S1, S2, S3, or the first, second and third vacuum jackets, are that a vacuum thermal insulating pipe receiving part J can be easily fabricated and also the solid heat transfer distance can be made longer this way. In FIG. 22 to FIG. 25, K designates a silicon sponge-made thermal insulating layer (thickness t=2 mm), H a plane heater, G a getter case, J a vacuum thermal insulating pipe receiving part, O a seal-off valve, Q a cable takeout opening, and OUT and IN are temperature measuring points. Furthermore, in FIG. 22 to FIG. 25, a 2 mm-thick stainless steel plate is used for the metal plate that constitutes vacuum jackets S1, S2, S3. The entire inner wall faces of the vacuum jackets S1 to S3 are given electroless Ag plating, and then a vacuum heating treatment of 550° C.×2 hrs is conducted on the silver plating layer to enhance its emissivity.
With FIG. 25, other temperature measuring points are shown beside temperature measuring points IN and OUT in the afore-shown FIG. 22 to FIG. 24. FIG. 26 and FIG. 27 show the results of temperature measurements at each measuring point of the first vacuum jacket S1 and the second vacuum jacket S2.
On the other hand, the thermal insulating performance of 2 vacuum thermal insulating boxes S can be demonstrated by the electric power required to hold the inside of the vacuum thermal insulating boxes S at the specified temperature used for comparison. First, the inventors of the present invention made adjustable the voltage to be applied to a plane heater H (100V·200 W·50Ω×2 pieces), and at the time when the temperature of the valve unit body V1 reached equilibrium (approx. 3 hours after the start of heating), power consumption was measured both under conditions when the vacuum thermal insulating box S was inserted, and the vacuum thermal insulating box S was not inserted, respectively.
It was learned that while input power was 81 W (stabilized at 150° C. at 45V, thus input power W=452/50×2=81 W) when the vacuum thermal insulating box S was inserted, input power was 213 W (stabilized at 150° C. at 73V, thus input power W=732/50×2=213 W) when the vacuum thermal insulating box S was not inserted. These results revealed that input power can be reduced to 81/213 owing to the thermal insulating performance of the vacuum thermal insulating box S.
Consumption power W, with which the thermal insulating performance of the afore-mentioned vacuum insulating box S is estimated, can be calculated by the operating time and operating voltage of the relay of the temperature controller that supplies power to the plane heater H because the power supplied to the plane heater H is proportional to the output voltage of the relay of the temperature controller. Thus, supply power to the plane heater H can be determined by measuring output voltage and output time of the relay of the temperature controller with an oscillogram, and by obtaining the peak area (the peak integration value) by making use of the integration function of the peak area of the oscillogram. Specifically, because the afore-mentioned peak area (a peak integration value) is equal to the output voltage×output time, it is determined that output time=the peak integration value/the output voltage, and the output %=output time×100/the measuring time=the peak integration value×100/(the measuring time×the output voltage).
For example, assuming that the output voltage of the relay of the temperature controller is 12V and the measuring time 50 seconds, it is determined that the output %=the peak integration value×100/(12×50)=the peak integration value/6.
According to test results, the peak integration value (the average of 5 points) of the oscillogram at the time when the temperature of the valve unit body V1 was in a stable state at 150° C., with the vacuum thermal insulating box S inserted, was 119.0 (V·sec) taking the average. Accordingly, the output % at this time becomes 119/6=19.83%. With a rated capacity of the plane heater H of 400 W, the output of the plane heater H becomes 400 W×19.83%=79.3 W. The peak integration value (the average of 5 points) of the oscillogram at the time when the temperature of the valve unit body V1 was in a stable state at 150° C., with the vacuum thermal insulating box S removed, was 331.6 (v·sec). Accordingly, the output % at this time becomes 331.6/6=55.27%. Thus, the output of the plane heater H becomes 400 W×55.27%=221.1 W.
When the input power ratio (the case where the vacuum thermal insulating box was in use/the case where the vacuum thermal insulating box was not in use=81/213) determined by the afore-mentioned voltage adjustment is compared with the output power ratio (79.3/221.1) determined by the peak integration value on the oscillogram, it was learned that there exists almost no difference between them. Because thermal insulating performance of a vacuum thermal insulating box S can be measured easier with the former method, wherein the input voltage to the plane heater H is adjusted, for embodiments of the present invention, the verification test for the vacuum insulating characteristics is conducted using the method of adjusting the input voltage.
In the case where the vacuum insulating box S, according to the combination of 3 vacuum jackets S1, S2, S3 is used as shown in FIG. 22 to FIG. 25, thermal insulating performance expressed by the ratio of input voltage to the plane heater H is 81/213, which is not a sufficient performance.
Another problem encountered is that the thermal insulating performance is lowered because the vacuum thermal insulating box S in FIG. 22 to FIG. 25 is structured by combining 3 segments, which leads to high thermal conductivity by solid heat transfer.
Furthermore, another problem with the afore-mentioned vacuum thermal insulating box S shown in FIG. 22 to FIG. 25 is that, because a 2 mm-thick stainless steel plate is employed from the view point of providing mechanical strength, thermal conductivity by solid heat transfer becomes relatively high.
Patent Document: TOKU-KAI-SHO No. 61-262295 Public Bulletin